Tetralogy of Fallot

Tetralogy of Fallot represents a combination of pulmonary stenosis and large ventricular septal defect. It is the most important malformation associated with persistent cyanosis, the commonest cause of "blue baby." The term "tetralogy" was suggested more than a century ago, when two other features (making a total of four) were considered central to this malformation. These two features are now known to be consequences of the first two.

The most essential component of this lesion is large ventricular septal defect. The obligatory high pressure in the right ventricle is, however, maintained by pulmonary stenosis rather than by high resistance in the pulmonary circulation, as is the case in isolated ventricular septal defect. The narrowing may be located either at the valve or below the valve (subvalvular pulmonary stenosis ). In some cases not only is the valve or the outflow segment of the right ventricle affected by the malformation, but the pulmonary artery may be smaller than average (hypoplastic ), compounding the difficulty in the pulmonary circulation. In most cases the resistance to outflow from the right ventricle is higher than that from the left ventricle—hence the reversal of blood flow (right-to-left shunt) resulting in cyanosis. When pulmonary stenosis is relatively mild, the usual left-to-right shunt through the ventricular septal defect takes place (noncyanotic tetralogy of Fallot). The wide variation in the resistances within the pulmonary outflow tract creates a range of skin coloration in children with tetralogy of Fallot—some showing normal color, others a faintly blue tinge, still others a deep purple color. In black children and other children with naturally dark skin, the effects of cyanosis may be less apparent. Despite the complexity of this malformation of the heart, survival beyond infancy is possible in most cases; development may be mildly impaired,

but many patients reach adulthood, some even surviving beyond middle age.

One of the most spectacular advances in treating congenital heart disease was the operation introduced in 1944 by Alfred Blalock and Helen Taussig. This procedure crafted a connection between the systemic circulation and the pulmonary circulation by suturing the large artery supplying the arm (brachial artery) into the pulmonary artery branch; the arterial blood, poorly oxygenated because of mixing with venous blood through the right-to-left shunt, could thereby return to the lungs for reoxygenation. The drama of deeply blue children assuming a pink color after the operation created a sensation when it was first performed. This operation is now rarely used since it does not attack the basic defect. Open-heart surgery allows surgeons to close the ventricular septal defect and dilate the right ventricular outflow tract; the procedure is performed on patients in infancy or early childhood.